Glucokinase (GK) is a member of a family of four hexokinases that are critical in the cellular metabolism of glucose. Specifically GK, also known as hexokinase IV or hexokinase D, facilitates glucose induced insulin secretion from pancreatic β-cells as well as glucose conversion into glycogen in the liver. GK has a unique catalytic activity that enables the enzyme to be active within the physiological range of glucose (from 5 mM glucose to 10 mM glucose).
Genetically modified mouse models support the role of GK playing an important role in glucose homeostasis. Mice lacking both copies of the GK gene die soon after birth from severe hyperglycemia, whereas mice lacking only one copy of the GK gene present with only mild diabetes. Mice that are made to overexpress the GK gene in their livers are hypoglycemic.
Numerous human mutations in the GK gene have been identified, with the vast majority of them resulting in proteins with impaired or absent enzymatic activity. These loss-of-function mutations are thought to contribute to the hyperglycemia seen with maturity-onset diabetes of the young type II (MODY-2). A small fraction of these mutations result in a GK with increased catalytic function. These individuals present with moderate to severe hypoglycemia.
GK activity in the liver is transiently regulated by glucokinase regulatory protein (GKRP). GK catalytic activity is inhibited when GK is bound to GKRP. This interaction is antagonized by increasing concentrations of both glucose and fructose-1-phosphate (F1P). The complex of the two proteins is localized primarily to the nuclear compartment of a cell. Post prandially as both glucose and fructose levels rise, GK released from GKRP translocates to the cytoplasm. Cytoplasmic GK is now free of the inhibitory effects of GKRP and able to kinetically respond to glucose. Evidence from the Zucker diabetic fatty rat (ZDF) indicates that their glucose intolerance may be a result of this mechanism failing to function properly.
A compound that acts directly on GKRP to disrupt its interaction with GK and hence elevate levels of cytoplasmic GK is a viable approach to modulate GK activity. Such an approach would avoid the unwanted hypoglycemic effects of over stimulation of GK catalytic activity, which has been seen in the development of GK activators. A compound having such an effect would be useful in the treatment of diabetes and other diseases and/or conditions in which GKRP and/or GK plays a role. The present invention provides compounds that bind GKRP and disrupts its interaction with GK.